Nonlinear optical devices of the second harmonic generator, the up/down frequency converter, or the optical parametric oscillator or the like can be manufactured by using the nonlinear optical effect of crystals. A laser produced from laser generator can be converted in its frequency by passing through a nonlinear optical device, whereby obtaining more lasers with useful wavelengths, allowing the laser generator finding wider applications. Among the nonlinear optical crystal materials, the halogen-containing nonlinear optical crystals are a kind of relatively special crystal materials. Because halogen ions have many similarities in coordination structures, their physical-chemical properties allow for avoiding a sudden change in the crystalline structure when the halogen ions replace with each other (partly or totally), and thus it is easy to achieve the modification of the materials.
At the same time, the focus topic has been put forth for the study and exploring of new nonlinear optical materials that exhibit high effect of second harmonic, broad transparent region, high damage threshold and stable physical-chemical properties. Currently, the main nonlinear optical materials include: BBO (β-BaB2O4), LBO (LiB3O5) crystal, CBO (CsB3O5) crystal, CLBO (CsLiB6O10) crystal and KBBF (KBe2BO3F2) crystal. Although the crystal growing techniques for these materials have been developed increasingly, there are still apparent disadvantages, such as, deliquescence tendence of the crystals, long period of growing, serious behavior of growing in layers as well as high price. Accordingly, it is still an important and hard work to seek new nonlinear optical crystal materials.
In order to make up the shortages of the nonlinear optical crystals mentioned above, scientists all over the world are still focusing highly on the study and research of various novel nonlinear crystals. They pay attention to not only the optical properties and mechanical properties of the crystals, but also the preparing properties of the crystals more and more. In the case of finding a useful nonlinear optical crystal, a laser with limited wavelength can be converted to a laser with a new wavelength range by using the nonlinear optical effects of second harmonic, frequency mixing and optical parametric oscillating or the like. By using this technique, it is possible to fill up the gap in the spectrum range of the laser wavelengths irradiated by various laser devices, and allow for the laser generator finding a wider application.